Hologram plate and its fabrication process

ABSTRACT

The invention provides a hologram plate which is used with the double-focus replication process, and which is integrated with a spacer to impart marring resistance thereto, and is integrated with a light absorbing layer to allow zero-order light and first-order light to have substantially the same intensity. This hologram plate  42  comprises an array of collective element holograms for diffracting parallel light incident thereon at a specific wavelength and a specific incident angle in such a way that the light is converged onto a specific focal length position. The hologram plate 42 is a multilayer structure made up of a first transparent substrate 31, a hologram layer 32, an adhesive layer 33 and a second transparent substrate 41. The second transparent substrate 42 defines a surface in contact with a hologram photosensitive material 53 during hologram replication.

BACKGROUND OF THE INVENTION

[0001] The present invention relates generally to a hologram ate and itsfabrication process, and more specifically to a hologram plate designedto replicate a hologram array comprising collective element hologramssuch as hologram color filters, and its fabrication process.

[0002] The present invention is also concerned with a multifacetedhologram plate and its fabrication process.

[0003] Further, the present invention is directed to the construction ofa protective film for a hologram plate.

[0004] In JP-A 06-222361, etc., the applicant has already come up with ahologram-harnessing color filter for the purpose of greatly increasingthe efficiency of utilization of liquid crystal display backlights, etc.This hologram color filter is basically made up of an array of atransmission type of collective element holograms capable of diffractingparallel light incident thereon at a specific wavelength and a specificangle of oblique incidence in such a way that it is converged on aspecific focal distance position.

[0005] To use such a hologram array as a hologram plate to replicateanother hologram array having similar properties by a hologramreplication process, for instance, a first hologram plate is fabricatedin the form of a computer-generated hologram (CGH). Then, the firsthologram plate is replicated by the hologram replication process tofabricate a hologram plate, from which the final product is fabricatedby a similar hologram replication process.

[0006] To replicate such a transmission type of collective elementhologram array as mentioned above, the applicant has filed a patentapplication (JP-A 09-90860) to come up with a process wherein whenreplicas of the first plate and hologram plate are fabricated, thedistance between the hologram plate and a hologram photosensitivematerial is fixed to substantially double the focal length of eachelement hologram to make a hologram replica having similar properties tothose of the hologram plate. This process is now explained withreference to FIG. 12.

[0007]FIG. 12 is illustrative of how to fabricate a hologram array 5providing a hologram color filter from a CGH array plate 7 in one singlereplication operation. A plate for a hologram array 5 providing ahologram color filter is constructed in the form of a CGH array 7. Thedistance from the relief surface of the CGH array plate 7 to aphotosensitive layer 13 is fixed to 2 f that is double the focal lengthf of each CGH 5″ so that a hologram photosensitive material 8 is spacedaway from the CGH array plate 7. Laser light 9 having a specificwavelength is entered into the CGH array plate 7 at a specific angle ofincidence, so that diffracted light 10, converged by the diffractionaction of each CGH 5″ from convergent light to divergent light, andstraightforwardly traveling transmitted light 11 interfere in thephotosensitive layer 13 of the hologram photosensitive material 8.

[0008] Here let D represent the diameter of a recording area of eachelement hologram 5″ of the CGH array plate 7. Then, the diffracted light10, once converged on a position P located at a distance f from therelief surface of each CGH 5″, is converged on a 2 f position into adivergent light beam having the same diameter D. Accordingly, if thedivergent light and the straitghtforwardly traveling transmitted light11 interfere in the photosensitive layer 13 located at this position,the diameter of the hologram interference fringe recording area becomesequal to D, and the pitch between adjacent replicated element hologramsbecomes equal to that between adjacent element holograms 5″ of the CGHarray plate 7 as well. In addition, when light traveling in the oppositedirection to the transmitted light for hologram array replication isentered in the thus replicated hologram array from the glass substrate12 side, the diffracted light is converged on a position P at a length ffrom the photosensitive layer 13 with hologram interference fringesrecorded therein, and so has the same diameter as the focal length ofeach element hologram 5″ of the CGH array plate 7. In other words, ahologram array completely identical with the CGH array plate 7 isobtained.

[0009] The hologram array replicated from the CGH array plate 7 in suchan arrangement as shown in FIG. 12 is then used as a hologram plate toobtain the end product. FIG. 13 is illustrative of one arrangement ofhow to carry out such second replication operation. In FIG. 13, H1stands for an intermediate hologram array obtained by replication in thearrangement of FIG. 12. This intermediate hologram array H1 is againused as a hologram plate for replication purposes. In this case, thehologram photosensitive material 8 is located on the side of the plate 7for the replication of the intermediate hologram array H1, andreconstructing illumination laser light 9′ is entered in theintermediate hologram array H1 from the opposite direction to thetransmitted light 11 for the replication of the intermediate hologramarray H1, and the distance from the diffraction surface of theintermediate hologram array H1 to the photosensitive layer 13 of thehologram photosensitive material 8 is fixed to 2 f that is double thefocal length f of each element hologram. When the reconstructingillumination laser light 9 is entered in the intermediate hologram arrayH1 in such an arrangement, light 10′ diffracted by each element hologramof the intermediate hologram array H1 travels in the opposite directionto the diffracted light 10 of FIG. 12 and, once converged, is convertedat the 2 f position to a divergent light beam having the same diameterD. Accordingly, diffracted light 10′ and straightforwardly travelingtransmitted light 11′ interfere in the photosensitive layer 13 locatedat this position as in the case of FIG. 12, so that an array of elementholograms having the same focal length f is replicated and recorded at apitch d in the area having the same diameter D.

[0010] The feature of this process is that a hologram similar inproperties to the hologram plate can be fabricated even when thehologram plate is in no perfect contact with the replica. In whatfollows, the hologram replication process in such an arrangement will becalled a double-focus replication process.

[0011] Incidentally, hologram photosensitive materials such asphotopolymers are generally poor in marring resistance whether in anunrecorded state or in a state subjected to post-recording treatments.When replication is carried out with a hologram plate in close contactwith a hologram photosensitive material, it is likely that the hologramon the hologram plate side is immediately damaged and some of thephotosensitive material on the replication side peels off, depositingonto the hologram on the hologram plate side. Such depositions arehardly removable.

[0012] When a hologram has such a focal length as mentioned above, thereis a variation in the focal length of replicas due to a contact gap atthe time of replication, and a variation in gap thickness leads to avariation in the focal length of replicas.

[0013] It is desired that the zero-order light and first-order lightdiffracted by the hologram plate have substantially the same intensityat the position of the hologram photosensitive material. To this end, itis required to place the refractive index modulation under severecontrol. However, this control is difficult on practical levels.

[0014] The hologram (intermediate hologram array HI) used for thereplication of the end products is herein called the hologram plate.When a hologram plate having only one hologram (hologram color filter)equivalent to one segment is used for the replication of such a colorfilter as mentioned above, however, replication efficiency becomesworse.

[0015] To avoid this, a process has been proposed in the art, whichprocess makes use of a hologram plate obtained by translating a CGHplate 7 with respect to one large hologram photosensitive material 8 fora plurality of replication cycles wherein, for instance, four or eightholograms are exposed to light to form four or eight juxtaposedholograms in the hologram photosensitive material, so that four or eightholograms can be simultaneously replicated in one replication operation.Such a hologram plate with a plurality of juxtaposed holograms is calleda multifaceted hologram plate.

[0016] As shown in FIG. 13, for instance, the multifaceted hologramplate is prepared in plural replication operations, using a CGH platewith respect to one large hologram photosensitive material. However,when at least one of plural exposure operations (replication operationsfrom the CGH plate) is improper, the resultant multifaceted hologramplate cannot be used or fails to provide a hologram plate having goodreplication efficiency.

[0017] In view of such prior art states as mentioned above, the firstobject of the present invention is to provide a hologram plate used withthe double-focus replication process, which is integrated with a spacerto impart marring resistance thereto, and is integrated with a lightabsorbing layer to allow zero-order light and first-order light to havesubstantially the same intensity, and its fabrication process.

[0018] The second object of the present invention is to provide amultifaceted hologram plate which can have hologram segments of improvedproperties, can be used for efficient replication, and has improveddurability, and its fabrication process.

[0019] The third object of the present invention is to provide an easilyreleasable protective film for a hologram plate, which prevents surfacemarring, wearing and contamination at the time of contact replication orremoval of foreign matters.

SUMMARY OF THE INVENTION

[0020] According to the present invention, the aforesaid first objet isachieved by the provision of a hologram plate comprising an array of atransmission type of collective element holograms that diffract parallellight incident thereon at a specific wavelength and a specific angle ofincidence in such a way that the parallel light is converged on aspecific focal length position, characterized by comprising a multilayerstructure made up of a first transparent substrate, a hologram layer, anadhesive layer and a second transparent layer, said second transparentsubstrate defining a surface into contact with a hologram photosensitivematerial when hologram replication is carried out.

[0021] Preferably in this case, the second transparent substrate shouldhave a thickness that is substantially twice the focal length of eachcollective element hologram, inclusive of the thickness of the adhesivelayer.

[0022] Preferably, a water-soluble protective layer should beinterleaved between the hologram layer and the adhesive layer.

[0023] Preferably in the case mentioned just above, the secondtransparent substrate should have a thickness that is substantiallytwice the focal length of each collective element hologram, inclusive ofthe thicknesses of the adhesive layer and water-soluble protectivelayer.

[0024] The diffraction efficiency of the hologram layer may be preset insuch a way as to allow the zero-order light and first-order lightdiffracted by the hologram layer to have substantially the sameintensity.

[0025] An absorbing layer may be interleaved at any desired positionbetween the hologram layer and the second transparent layer, and a lightabsorbing material is dispersed throughout the absorbing layer in such away as to allow the zero-order light and first-order light diffracted bythe hologram layer to have substantially the same intensity.

[0026] An absorbing layer may be located on the surface of the secondtransparent substrate, and a light absorbing material is dispersedthroughout the absorbing layer in such a way as to allow the zero-orderlight and first-order light diffracted by the hologram layer to havesubstantially the same intensity.

[0027] According to the present invention, there is also provided aprocess for fabricating the hologram plate for the purpose of achievingthe aforesaid first object of the present invention, characterized inthat:

[0028] said adhesive layer comprises an ultraviolet curing adhesiveagent,

[0029] said multilayer structure, obtained by forming said hologramlayer on said first transparent substrate and then superposing saidsecond transparent substrate on said hologram layer with an uncuredultraviolet curing adhesive agent interleaved therebetween, is spun tospin an extra portion of said adhesive agent out of the peripherythereof, thereby making said adhesive layer uniform, while the rpm ofsaid multilayer structure is controlled to obtain a desired thickness,and

[0030] said multilayer structure is irradiated with ultravioletradiation through said first transparent substrate or said secondtransparent substrate to cure said adhesive agent.

[0031] Preferably in this case, the hologram layer is exposed top-polarized light. P-polarized light is more reduced in interfacereflection than s-polarized light, so that unnecessary interferencefringes can be reduced during exposure and Δn (refractive indexmodulation) can be controlled to a reduced value as well.

[0032] However, when the diffraction efficiency of the CGH plate is toolow as an example, the use of s-polarized light is preferable because Δncan be increased with an increased diffraction efficiency.

[0033] In the present invention for the purpose of achieving theaforesaid first object, the hologram plate comprises a multilayerstructure made up of a first transparent substrate, a hologram layer, anadhesive layer and a second transparent layer and the second transparentsubstrate defines a surface in contact with a hologram photosensitivematerial during hologram replication, so that the second transparentsubstrate can function as a protective layer to make the hologram plateresistant to marring. In addition, the second transparent substrate canbe used as a spacer for a double-focus replication process wherein thedistance between the hologram plate and the hologram photosensitivematerial is set at substantially double the focal length of eachcollective element hologram, so that replicas can be fabricated withconstant focal lengths.

[0034] An absorbing layer is located between the hologram layer and theadhesive layer or at other position to allow the zero-order light andfirst-order light diffracted by the hologram layer to have substantiallythe same intensity, so that hologram replicas of high diffractionefficiency can be obtained.

[0035] The present invention has been described with reference to thedouble-focus fabrication process. It is noted, however, that it isactually important and desirous to keep the distance between thehologram plate and the photosensitive material constant in considerationof the total thickness of all members inclusive of the adhesive layer,protective layer and index matching liquid.

[0036] When the first replication is carried out in the contact mode andthe second is carried out by the double-focus replication process, it isdesired that the distance coincide with the value obtained by thesubtraction of the first replication gap from the value double the focallength.

[0037] The aforesaid second object of the present invention is achievedby the provision of a hologram plate comprising a plurality ofjuxtaposed unit hologram segments, characterized in that:

[0038] one common transparent thin sheet is provided over the surfacesof said plurality of juxtaposed unit hologram segments with an adhesiveagent interleaved therebetween.

[0039] Preferably in this case, each unit hologram segment shouldcomprise a transparent substrate, a photosensitive material layer formedthereon while a hologram is recorded therein, and a protective layerformed on said photosensitive material layer.

[0040] It is here preferable that a transparent thin sheet should bebonded onto said protective layer for each unit hologram segment.

[0041] It is also preferable that said plurality of unit hologramsegments should be hologram segments replicated from the same hologramplate.

[0042] Each unit hologram segment, for instance, may be a hologram colorfilter.

[0043] Regarding the aforesaid second object of the present invention,there is provided a process for fabricating a hologram plate comprisinga plurality of juxtaposed unit hologram segments and one commontransparent sheet provided over the surfaces of said unit hologramsegments with an adhesive agent interleaved therebetween, characterizedby comprising steps of:

[0044] preparing a plurality of unit hologram segments,

[0045] adsorbing a transparent thin sheet onto the surface of areference plate and laminating said plurality of unit hologram segments,in juxtaposed relation to each other, on said transparent thin sheetwith an adhesive agent interleaved therebetween,

[0046] bonding a base plate onto the back side of said plurality ofjuxtaposed unit hologram segments with an adhesive agent interleavedtherebetween, and

[0047] desorbing said transparent thin sheet from said reference plateto release said transparent thin sheet from said reference plate.

[0048] Preferably in this process, at the step of preparing a pluralityof unit hologram segments, said plurality of unit hologram segments arereplicated from the same hologram plate.

[0049] According to the present invention for achieving the aforesaidsecond object, all the unit holograms can be precisely replicatedbecause the unit hologram segments are kept flush with one another byone common thin sheet glass provided over the plurality of juxtaposedunit hologram segments. When the hologram photosensitive material isbrought into close contact with the multifaceted hologram plate with anindex matching liquid applied therebetween for the purpose of hologramreplication, it is extremely unlikely that an optical adhesive agentbetween adjacent unit hologram segments will be dissolved in the indexmatching liquid. If a glass sheet is used as the transparent thin sheet,improved durability is then obtained. Fabricated by the lamination ofonly unit hologram segments put in good alignment with good properties,the multifaceted hologram plate according to the present invention forachieving the aforesaid second object have all unit hologram segments ofgood quality and uniform properties, and so can be used for hologramreplication with high efficiency.

[0050] According to the present invention for achieving the aforesaidthird object, there is provided a hologram plate comprising a hologramlayer with interference fringes formed thereon, a first layer capable ofbeing removed with water or a solvent, which is provided on the surfaceof said hologram layer or a transparent layer formed thereon, and asecond layer of a curing resin capable of being cured by light or heat,which is formed on said first layer.

[0051] In this hologram plate, the hologram layer may be either anamplitude type hologram layer with a metal film patterned thereon or ahologram layer comprising a hologram photosensitive material layer withinterference fringes recorded therein.

[0052] The first layer may have the property of absorbing light.

[0053] This hologram plate may be applied to either a transmission typehologram or a reflection type hologram.

[0054] Thus, the hologram plate for achieving the aforesaid third objectof the present invention comprises a hologram layer with interferencefringes formed thereon, a first layer capable of being removed withwater or a solvent, which is provided on the surface of said hologramlayer or a transparent layer formed thereon, and a second layer of acuring resin capable of being cured by light or heat, which is formed onsaid first layer. The second layer functions as a protective layer forthe hologram layer 202, thereby preventing the marring, wearing andcontamination of the hologram layer, which may otherwise occur at stepsof coating an index matching liquid, carrying out contact replication,removing the index matching liquid, removing foreign matters, and so on.As many holograms are replicated, the second layer, too, is subjected tomarring, wearing and contamination. In this case or, for instance, whenone fails to form the first layer or the second layer, the hologramplate is washed with water or boiled in boiling water, so that theprotective layer can be easily removed. Then, if fresh first and secondlayers are provided on the hologram layer, the hologram plate can beregenerated.

[0055] Still other objects and advantages of the invention will in partbe obvious and will in part be apparent from the specification.

[0056] The invention accordingly comprises the features of construction,combinations of elements, and arrangement of parts which will beexemplified in the construction hereinafter set forth, and the scope ofthe invention will be indicated in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0057]FIG. 1 is illustrative of an arrangement of how to replicate ahologram from a CGH array plate according to the first embodiment of theinvention.

[0058]FIG. 2 is illustrative of an arrangement of how to fabricate ahologram plate according to the first embodiment from the hologramreplica of FIG. 1.

[0059]FIG. 3 is illustrative of an arrangement of how to fabricate theend hologram replica from the hologram plate of FIG. 1 by thedouble-focus replication process.

[0060]FIG. 4 is illustrative of an arrangement of how to fabricate ahologram plate according to the second embodiment from the hologramreplica of FIG. 1.

[0061]FIG. 5 is a sectional view of the first step of the process forfabricating a hologram plate for the purpose of achieving the secondobject of the invention.

[0062]FIG. 6 is a sectional view of a step subsequent to FIG. 5.

[0063]FIG. 7 is a sectional view of a step subsequent to FIG. 6.

[0064]FIG. 8 is a sectional view of a step subsequent to FIG. 7.

[0065]FIG. 9 is a sectional view of a step subsequent to FIG. 8.

[0066]FIG. 10 is a sectional view of a multifaceted hologram plateaccording to one embodiment of the invention.

[0067]FIG. 11 is illustrative of how to fabricate a transmission typehologram using the hologram plate of the invention for the purpose ofachieving the third object of the invention.

[0068]FIG. 12 is illustrative of an arrangement of how to fabricate ahologram replica from a CGH array plate by a conventional double-focusreplication process.

[0069]FIG. 13 is illustrative of an arrangement of how to again makereplication using a hologram replica obtained in the arrangement of FIG.12 as a hologram plate.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0070] Embodiments of the hologram plate according to the presentinvention and its fabrication process are now explained.

[0071] In the first embodiment of the present invention, the firsthologram plate was fabricated in the form of a relief typecomputer-generated hologram (CGH) comprising an array of a transmissiontype of divergent element holograms. To fabricate this relief type CGH,the inference fringes of the divergent element holograms were firstcomputed by means of a computer in such as a way that laser light of 488nm wavelength, incident thereon at an incident angle of 40°, wasdiverged from a 50 μm focal length position on the incident side. Then,the interference fringes were rendered by means of electron beams on thesurface of a glass substrate on which, for instance, an electron beamresist was coated, followed by development. In FIG. 1, the CGH arrayplate is shown at 21, the element holograms at 22, and a relief surfaceat 23.

[0072] On the other hand, a hologram photosensitive material in the formof a photosensitive material 32, viz., photopolymer HRF600X made by DuPont was applied onto a glass substrate 31, viz., a 1737 glass substrateof 1.1 mm in thickness, made by Corning, thereby obtaining a hologramphotosensitive material 33.

[0073] If required, a water-soluble protective layer formed of PVA(polyvinyl alcohol), etc. may be coated on the photosensitive layer 32.This protective layer acts as a barrier layer for preventing theadhesive layer 37 to be referred to later from diffusing into thephotosensitive layer 32, resulting in adverse influences such as alowering of the degree of refractive index modulation, the swelling ofthe interference fringes, etc.

[0074] Then, the photosensitive layer 32 of the hologram photosensitivematerial 33 was brought into close contact with the relief surface 23 ofthe CGH array plate 21. P-polarized argon laser light 34 of 488 nmwavelength was entered at an incident angle of 40° into the resultantmultilayer structure from the back side of the CGH array plate 21(facing away from the relief surface 23) to allow divergent diffractedlight 35 diffracted by each element hologram 22 of the CGH array plate21 to interfere with straightforwardly traveling transmitted light 36 inthe photosensitive layer 32 of the hologram photosensitive material 33,thereby replicating a hologram from the CGH array plate 21. If, in thiscase, p-polarized light is used as the laser light 34, it is thenpossible to reduce reflections at the interface between the hologramphotosensitive material 33 and the plate 21, the interface between thehologram photosensitive material 33 and air, etc., thereby preventingunnecessary interference fringes from being recorded.

[0075] After the photosensitive layer 32 had been exposed to light in agiven fashion, an adhesive agent, viz., an ultraviolet curing adhesiveagent 37 and a glass plate 41 acting as a spacer were placed on thephotosensitive layer 32, as shown in FIG. 2. Then, the resultantmultilayer structure was spun by means of a spinner to spin an extraportion of the adhesive agent 37 out of the periphery thereof, so thatthe adhesive layer 34 was made uniform, while the rpm of the spinner wascontrolled to obtain the desired thickness. In this way, the glass plate41 was laminated on the photosensitive layer 32. Glass D263 of 100 μm inthickness, made by Shot, was used for the glass plate 41 and the spinnerwas spun at a fixed 2,800 rpm.

[0076] Thereafter, the adhesive agent 37 was cured by ultravioletirradiation through the glass substrate 31 or the glass plate 41.

[0077] Then, the end product was obtained by the aforesaid double-focusreplication process from the thus obtained hologram plate 42 comprisinga hologram array integrated with the spacer glass plate 41. FIG. 3 isillustrative of an arrangement of how to carry out such secondreplication operation. According to the arrangement of FIG. 3, thehologram array 33 integrated with the spacer glass plate 41 by means ofthe adhesive agent 37 is used as the hologram plate 42, and aphotosensitive material 53 is prepared by the application onto a glasssubstrate 51 of a hologram photosensitive material in the form of aphotosensitive layer 52, viz., photopolymer HRF600X made by Du Pont. Thephotosensitive layer 52 of the hologram photosensitive material 53 isbrought into close contact with the spacer glass sheet 41 of thehologram plate 42. Then, p-polarized argon laser light 54—that has thesame wavelength as that of the illumination light 34 for the replicationof the hologram array of hologram plate 42 and travels in the oppositedirection thereto—is entered at the same incident angle of 40° into thehologram plate 42 now from the glass substrate 31. Then, diffractedlight 55—that is diffracted by each element hologram of the hologramplate 42 and diverged upon converging onto the focal point—is allowed tointerfere with straightforwardly traveling transmitted light 56 in thephotosensitive layer 52 of the hologram photosensitive material 53 forreplication purposes. The p-polarized light is used for the same reasonas mentioned above. In the embodiment, each element hologram of thehologram array of hologram plate 42 has a focal length of 50 μm whereasthe spacer glass plate 41 has a thickness of 100 μm that is just doublethe focal length of each element hologram of the hologram plate 52.Thus, the focal length of each element hologram of the replica, too, canbe regulated to accurately 50 μm by the double-focus replicationprocess.

[0078] More preferably in this embodiment, the thickness of the spacerglass plate 42 inclusive of the thickness of the adhesive agent 37 andthe thickness of the absorbing layer 57 (FIG. 4) to be referred to latershould be just double the focal length of each element hologram.

[0079] The hologram plate 42 used with such a double-focus replicationprocess, because of using the glass plate 41 as the spacer, was soimproved in terms of marring resistance that it could be used forhologram replication over and over. In the process of hologramreplication, some of the hologram photosensitive material 53 wasdeposited onto the hologram plate 42. However, this hologram plate 42could easily be washed by conventional scrubbing without causing damagethereto.

[0080] The second embodiment of the invention is now explained. As shownin FIG. 1, the CGH array plate 21 is used as the hologram plate 42. Asin the first embodiment, divergent diffracted light 35 diffracted byeach element hologram 22 in the CGH array plate 21 is then allowed tointerfere with straightforwardly traveling transmitted light 36 in thephotosensitive layer 32 of the hologram photosensitive material 33 tofabricate a hologram replica of the CGH array plate 21. After exposureof the photosensitive layer 32 to light in a given fashion, as shown inFIG. 4, the photosensitive layer 32 was coated thereon with aconcentration-controlled polyvinyl alcohol solution in which a red dyecapable of absorbing light of 488 nm wavelength was dissolved dependingon the ratio of zero-order light 56 and first-order light 55 diffractedby the hologram in the photosensitive layer 32 to form an absorbinglayer 57 thereon. Following this, the adhesive agent, viz., theultraviolet curing adhesive agent 37 and the glass plate 41 acting as aspacer were placed on the absorbing layer 57, as in the firstembodiment. Then, the resultant multilayer structure was spun by meansof a spinner to spin an extra portion of the adhesive agent 37 out ofthe periphery thereof, so that the adhesive agent 34 layer was madeuniform, while the rpm of the spinner was controlled to obtain thedesired thickness, thereby laminating the glass plate 41 on theabsorbing layer 57 whereupon the adhesive agent 37 was cured byultraviolet irradiation thorough the glass substrate 31 or the glassplate 41. Finally, as in the first embodiment, the end product of highdiffraction efficiency could be obtained by the double-focus replicationprocess according to the arrangement of FIG. 3.

[0081] In this case, the absorbing layer 57 acts as follows. Usually,the zero-order light 56 is higher in intensity than the first-orderlight 55, and so is less susceptible to efficient interference even whenit interferes with the latter in the photosensitive layer 52. However,the optical path taken by the zero-order light 56 in the absorbingmedium is longer than that by the first-order light 55, because thezero-order light 56 transmits obliquely through the absorbing layer 57whereas the first-order light 55 transmits almost vertically as comparedwith the zero-order light 56. By control of the concentration andthickness of the absorbing layer 57, it is thus possible to decay thezero-order light 56 of higher intensity in a larger proportion and,hence, make the zero-order light 56 and first-order light 55 havesubstantially the same intensity upon arrival at the photosensitivelayer 52, so that they can interfere with each other with highefficiency. It is thus possible to obtain replicas of high diffractionefficiency.

[0082] It is here noted that the absorbing layer 57 may be locatedbetween the glass plate 41 and the adhesive agent 37 or on the side ofthe glass plate 41 that faces away from the glass substrate 31, to saynothing of the FIG. 4 position.

[0083] Alternatively, it is acceptable to dispense with such anabsorbing layer 57. In this case, however, it is required to regulatethe ratio of the zero-order light and the first-order light diffractedby the hologram in the photosensitive material 32 to substantially 1:1by some post-exposure treatments of the photosensitive layer 32. Forinstance, when photopolymer HRF600X made by Du Pont is used, it is heattreated at 120° C. for 2 hours after exposure to bring the diffractionefficiency of the first-order light up to almost 100%. However, if thisheat treatment is carried out at 120° C. for 10 minutes, it is thenpossible to fix the diffraction efficiencies of the zero-order light andfirst-order light to substantially 50% and 50%, respectively. It is herenoted that by curtailing the post-exposure heat-treatment time asmentioned above, it is also possible to reduce changes in the angles ofinclination of interference fringes due to the deformation of thehologram photosensitive material which may occur by long-term heating,variations in the interference fringe plane, etc.

[0084] When the absorbing layer 57 is provided, it is possible toregulate the ratio of the zero-order light and the first-order light tosubstantially 1:1 by means of (1) thickness control of the absorbinglayer 57, (2) control of heat-treatment conditions, (3) thicknesscontrol of the photosensitive layer 32, etc. Particularly preferredcontrol can be achieved by (1) combined with (3). In this case, it ispossible to determine the properties of the absorbing layer 57 in viewof the ratio of the zero-order light and the first-order light after thepost treatment and, hence, gain more accurate control.

[0085] Regulation of the ratio of the zero-order light and thefirst-order light diffracted by the hologram in the photosensitive layer32 to substantially 1:1 may also be achieved by reducing the thicknessof the photosensitive layer 32 in the absence of the absorbing layer 57.For instance, when photopolymer HRF600X made by Du Pont is used, thediffraction efficiency of the first-order light may be regulated tosubstantially 100% by an ordinary post treatment at a thickness of 4.0μm. However, if this thickness is reduced down to 2.0 μm, it is thenpossible to fix the diffraction efficiencies of the zero-order light andthe first-order light to substantially 50% and 50%, respectively.

[0086] In the aforesaid embodiments, an array comprising divergentelement holograms is used for the CGH array plate 21 so as to obtain ahologram array of hologram plate 42 from the CGH array plate 21 by acontact hologram replication process. However, when a hologram array ofhologram plate 42 is obtained from the CGH array plate 21 by thedouble-focus replication process as in the case of FIG. 5, an array ofcollective element holograms should be used for the CGH array plate 21.

[0087] The hologram plate and its fabrication process for achieving thefirst object of the present invention have been described with referenceto the first and second embodiments, respectively. Next, the hologramplate and its fabrication process for accomplishing the second object ofthe present invention are explained with reference to some embodiments.

[0088] FIGS. 5 to 10 are sectional views illustrative of a sequence ofsteps for carrying out the process for fabricating the hologram plateaccording to the first embodiment of the present invention for achievingthe second object thereof.

[0089] A plurality of holograms are fabricated from such a CGH plate(the first plate) 7 as shown in FIG. 12 in one replication operation. Tothis end, a photopolymer or other photosensitive material layer 102,formed on a substrate glass 101 of hologram size, is provided thereonwith a PVA (polyvinyl alcohol) layer 103 acting as a combined protectivelayer and coloring layer for preventing the occurrence of unnecessaryinterference fringes due to multiple interferences to prepare aphotosensitive material, as shown in FIG. 5. This hologramphotosensitive material is brought into close contact with the CGH arrayplate 7 or spaced away therefrom at a distance double the focal length fas shown in FIG. 12. Replicating illumination light (corresponding tothe laser light 9 in FIG. 12) is entered into the resultant multilayerstructure from the CGH plate 7 side in the case where the CGH plate 7 isof the transmission type, and the hologram photosensitive material sidein the case where the CGH plate 7 is of the reflection type to allowtransmitted light and diffracted light in the case where the CGH plate 7is of the transmission type, and incident light and diffracted light inthe case where the CGH plate 7 is of the reflection type to interfere inthe photosensitive material layer 102, thereby making a hologram replicaof the CGH plate 7.

[0090] Then, as shown in FIG. 6, a thin sheet glass 105 is laminated onthe PVA layer 103 of each hologram photosensitive material with ahologram replica of the CGH plate 7, using an optical adhesive agent104, thereby preparing a plurality of unit hologram plates 120 havingsimilar properties. When the double-focus replication process is used inthis case, the total thickness of the PVA layer 103, optical adhesiveagent 104 and thin sheet glass 105 should preferably be less than thefocal length f.

[0091] Then, as shown in FIG. 7, a thin sheet glass 121 having a largearea is brought into vacuum contact with the optical flat surface of areference glass 130. When the double-focus replication process is used,the thickness of the thin sheet glass 121 should preferably be less thanthe focal length f. Using an optical adhesive agent 122, a plurality ofunit hologram plates 120 in alignment are then laminated on the thinsheet glass 121 with the same force and height.

[0092] If, after the step of FIG. 6, the four side edge faces of theunit hologram plates 120 are cut out by dicing or other cutting means,and especially if the end faces of the substrate glass 101,photosensitive material layer 102, PVA layer 103, optical adhesive agent104 and thin sheet glass 105 are cut out to put them in good alignment,air bubbles are less likely to penetrate in between adjacent unitholograms 120 at the lamination step of FIG. 7, and alignment precisionis further improved.

[0093] Using an optical adhesive agent 124, a base glass 123 is bondedto the back sides of the unit hologram plates 120 put in alignment, asshown in FIG. 8, for the purposes of reinforcement and preventingpenetration of a solvent (an index matching liquid) in between adjacentunit hologram plates 120. Preferably in this case, the gap betweenadjacent unit hologram plates 120 should be filled up with the opticaladhesive agent 124. This is because an unfilled gap between adjacentunit hologram plates 120 may possibly lead to unnecessary interferencefringes due to reflection and scattering at that gap upon obliqueincidence of replicating illumination light.

[0094] After the optical adhesive agent 124, etc. have been full-cured,the thin sheet glass 121 is desorbed and released from the referenceglass 130 brought into vacuum contact therewith, as shown in FIG. 10, sothat a multifaceted hologram plate 125 of such shape in section as shownin FIG. 10 can be obtained in finished form according to one embodimentof the present invention.

[0095] With the multifaceted hologram plate 125 according to the presentinvention, all the unit holograms can be precisely replicated becausethe unit hologram plates 120 are kept flush with one another by onecommon thin sheet glass 121 provided over the unit hologram plates 120put in good alignment. When the hologram photosensitive material isbrought into close contact with the multifaceted hologram plate 125 withan index matching liquid applied therebetween for the purpose ofhologram replication, it is extremely unlikely that the optical adhesiveagent 122 between adjacent unit holograms 120 will be dissolved in theindex matching liquid (e.g., xylene) because the thin sheet glass 121 isprovided over the multifaceted hologram plate 125.

[0096] Fabricated by the lamination of only unit hologram plates 120 putin good alignment with good properties, the multifaceted hologram plate125 according to the present invention have all unit hologram plates ofgood quality and uniform properties, and so can be used for hologramreplication with high efficiency.

[0097] Regarding the aforesaid embodiment, it is noted that the PVAlayer 103 or thin sheet glass 105 may be omitted from the unit hologramplate 120.

[0098] It is also noted that the hologram to be replicated may be ofeither the transmission or the reflection type, and that it is notalways necessary to replicate the multifaceted hologram plate 125 by thedouble-focus replication process.

[0099] The hologram plate for achieving the third object of the presentinvention is now explained.

[0100] A transmission type hologram is recorded by entering object lightand reference light in a hologram dry plate from the same side andallowing both for interference in a hologram photosensitive materiallayer of the hologram dry plate. The thus recorded transmission typehologram or a transmission type computer-generated hologram(transmission type CGH) obtained by computing interference fringes bymeans of a computer, and rendering the interference fringes by means ofelectron beams to form the interference fringes on a substrate byphotolithography is used as a transmission type hologram plate. Anotherhologram dry plate is brought into close contact with or spaced slightlyaway from the side of the transmission type hologram plate that facesaway from the reconstructing illumination light incident side thereof.Replicating illumination light corresponding to the reconstructingillumination light is entered in the resultant multilayer structure fromthe hologram plate to allow diffracted light corresponding to the objectlight and transmitted light corresponding to the reference light tointerfere in the hologram photosensitive material layer of the hologramdry plate, so that a transmission type hologram similar properties tothe hologram plate is replicated.

[0101] A reflection type hologram is recorded by entering object lightand reference light in a hologram dry plate from opposite sides to allowboth to interfere in a hologram photosensitive material layer of thehologram dry plate. The thus recorded reflection type hologram is usedas a reflection type hologram plate. Another hologram dry plate isbrought into close contact with or spaced slightly away from the side ofthe reflection type hologram plate, on which reconstructing illuminationlight is incident. Replicating illumination light corresponding to thereconstructing illumination light is entered in the multilayer structurefrom the hologram dry plate side to allow diffracted light correspondingto object light and the replicating illumination light corresponding toreference light to interfere in the hologram photosensitive materiallayer of the hologram dry plate, so that a reflection type hologramsimilar in properties to the hologram plate is replicated.

[0102] The thus replicated transmission type hologram or reflection typehologram is used as a fresh hologram plate for similar replication,whereby a number of transmission or reflection type holograms havingsimilar properties can be fabricated.

[0103] However, such a hologram plate as mentioned above which, unlessotherwise stated, is understood to include both a transmission typehologram plate and a reflection type hologram plate—is susceptible tosurface marring, wearing and contamination as it is repeatedly used forreplication. Such defects are caused by repeated contact of the hologramplate with a hologram dry plate using a photopolymer or the like as ahologram photosensitive material or a spacer used in a hologramreplication process using such a spacer (FIGS. 12 and 13). For thisreason, a protective film is generally provided over the surface of thehologram plate. However, this protective layer, too, is damaged bymarring, wearing and contamination to such a degree that it can nolonger be used, as it is used over an extended period.

[0104] The third object of the present invention is to provide an easilyreleasable, hologram plate-protecting film for preventing surfacemarring, wearing and contamination which may otherwise occur in thecontact replication process or when foreign matters are removed. Oneembodiment of the present invention in this regard is now explained.

[0105]FIG. 11 is a sectional view of how to replicate a transmissiontype hologram using the hologram plate according to this embodiment. Astypically set forth in JP-A's 11-6917 and 11-271535, a hologram plate210 is prepared by forming a metal film 202 formed of Cr on atransparent substrate 201 and using electron beams to patterninterference fringes for a hologram color filter as an example by meansof photolithography, thereby forming an amplitude typecomputer-generated hologram pattern 205 thereon.

[0106] Then, the metal film 202 with such an amplitude typecomputer-generated hologram pattern 205 formed thereon is providedthereon with a first layer 203 capable of being removed by water or asolvent according to the present invention. Finally, the first layer 203is provided thereon with a second layer 204 formed of a curing resincapable of being cured by light or heat. In this way, the transmissiontype hologram plate 204 according to the present invention isfabricated.

[0107] In this embodiment, the second layer 204 formed on the surface ofthe hologram plate 210—which surface comes into close contact with ahologram dry plate 220 or the like functions as a protective layer forthe finely patterned hologram layer 202, thereby preventing the marring,wearing and contamination of the hologram layer 202, which may otherwiseoccur at steps of coating an index matching liquid, carrying out contactreplication, removing the index matching liquid, removing foreignmatters, and so on.

[0108] The light or heat-curable resin layer 204 is usually of highhardness. However, as many holograms are replicated, the protectivelayer 204, too, is subjected to marring, wearing and contamination atthe steps of coating an index matching liquid, carrying out contactreplication, removing the index matching liquid, removing foreignmatters, and so on.

[0109] In this case or, for instance, when one fails to form the firstlayer 203 or the second layer 204, the hologram plate 210 is washed withwater or boiled in boiling water, so that the protective layer 204 canbe easily removed because the first layer 203 is dissolved in water orboiling water. Then, if fresh first and second layers 203 and 204 areprovided on the hologram layer 202, the hologram plate 210 can then beregenerated.

[0110] This embodiment of the present invention is now explained withreference to one specific example. A hologram plate 210 was prepared byforming an about 0.05 μm thick Cr film 202 on a quartz substrate 201(n=1.46) and rendering and patterning interference fringes for a colorfilter by means of photolithography using electron beams to form ahologram pattern 205.

[0111] On the other hand, 0.8% by weight of a red dye (Kayafect RedG.C.I. Direct R-23, Nippon Kayaku Co., Ltd.) wad added to and dissolvedin a 10% (solid content) aqueous solution of polyvinyl alcohol toprepare a colored aqueous polyvinyl alcohol solution. By means of spincoating, this aqueous solution was coated on the Cr film 202 of thehologram plate 210 with the hologram pattern 205 formed thereon, andthen dried at room temperature for 1 hour and 70° C. for a further 1hour to obtain a light absorbing layer 203 of about 1 μm in thickness.This light absorbing layer 203 had a refractive index of n=1.52.

[0112] Then, an ultraviolet curing resin (Seikabeam EXG-75-1, DainichiSeika Industries, Ltd.) was coated on the light absorbing layer 203 bymeans of spin coating, then dried at 60° C. for 1 hour, then irradiatedwith 2,000 mJ ultraviolet radiation from an ultraviolet lamp includingall wavelength components 250 nm, 330 nm and 360 nm to cure the resin,and finally dried at 70° C. for 2 hours to bring the formation of aprotective layer 204 of about 2 μm in thickness to completion. Theultraviolet-cured resin layer 204 had a refractive index of n=1.53.

[0113] The thus fabricated hologram plate 210 was used for thereplication of a hologram color filter in the arrangement of FIG. 11. Tothis end, a hologram dry plate 220 is prepared by laminating a hologramphotosensitive material layer 222 comprising a photopolymer on atransparent substrate 221 and laminating a protective layer 223 on thesurface of the layer 222. The protective layer 204 of the hologram plate210 is brought into close contact with the protective layer 223 of thehologram dry plate 220 with an index matching liquid 215 interleavedtherebetween while a prism 211 having an inclined surface 212 is broughtinto close contact with the back surface of the hologram plate 210.Laser light of 514 nm wavelength is entered in the inclined surface 212to enter replicating illumination light 230 in the hologram layer 202 ofthe hologram plate 210 at a large angle of incidence.

[0114] Zero-order transmitted light 231, first-order diffracted light232 and second-order diffracted light 233 are generated from thehologram pattern 205. However, the zero-order transmitted light 231 andsecond-order diffracted light 233 are higher in attenuation factor thanthe first-order diffracted light 232, because the first-order diffractedlight 232 is almost vertical with respect to the hologram layer 202whereas the zero-order transmitted light 231 and second-order diffractedlight 233 have a large angle of diffraction with respect to the hologramlayer 202 and so the length of an optical path passing through the lightabsorbing layer 203 becomes relatively long with respect to thezero-order diffracted light 231 and second-order diffracted light 233.Of the zero-order transmitted light 231, first-order diffracted light232 and second-order diffracted light 233, the zero-order transmittedlight 231 has the highest light intensity and the second-orderdiffracted light 233 has the lowest light intensity. Through the actionof this light absorbing layer 203, it is thus possible to make theintensities of the zero-order transmitted light 231 and first-orderdiffracted light 232 substantially equal to each other upon arrival atthe hologram photosensitive material layer 222 of the hologram dry plate220 and, hence, reduce the relative intensity of the second-orderdiffracted light 233 extremely. Thus, the insertion of the lightabsorbing layer 203 in the hologram plate 210 makes unnecessaryinterference fringes due to the second-order diffracted light 233unlikely to occur. The zero-order transmitted light 231, first-orderdiffracted light 232, second-order diffracted light 233, etc. attenuatedthrough the light absorbing layer 203 are again incident on the hologramlayer 202 after Fresnel reflection at interfaces of the hologram dryplate 220 (the surface of the protective layer 223, the interfacebetween the protective layer 223 and the hologram photosensitivematerial layer 222, the interface between the hologram photosensitivematerial layer 222 and the transparent substrate 221, and the backsurface of the transparent substrate 221). However, the reflected lightis attenuated through the light absorbing layer 203 and its lightintensity is sufficiently reduced upon arrival at the hologramphotosensitive material layer 222. Thus, unnecessary interferencefringes due to the reflected light from these interfaces, too, areunlikely to occur because of the presence of the light absorbing layer203.

[0115] The zero-order transmitted light 231 and first-order diffractedlight 232 generated from the hologram plate 210 interfere in thehologram photosensitive material layer 222 of the hologram dry plate220, so that a transmission type hologram similar in diffractionproperties to the hologram plate 210 is replicated in the hologram dryplate 220.

[0116] A hologram plate with no protective layer provided thereon issusceptible to marring. For instance, a fine patterning (205) brokendown in the process of about 500 replication cycles. However, a hologramplate with such a protective layer 204 provided thereon according to thepresent invention could stand up to 10,000 or more replication cycles.This protective film, even when more or less damaged, had no adverseinfluence on replication because the refractive index of the ultravioletcuring resin layer 204 was nearly equal to that of the index matchingliquid 215 (cardinal oil; n=1.515). Removal of the protective layer 204is achieved by placing and boiling the hologram plate 210 in boilingwater to dissolve the light absorbing layer 203 therein. The merit ofthis method is that no access to the patterned surface 205 is needed. Byremoving and regenerating the protective layer 204 per 10,000replication cycles, the hologram plate 210 could be protected on asemi-permanent basis.

[0117] While the hologram plate for achieving the third object of thepresent invention has been described with reference to its specificembodiment and example, it is understood that the present invention isnot limited thereto, and so many modifications may be made. The hologramplate of the present invention is applicable to not only thetransmission type but also the reflection type. It is also understoodthat the first layer 203 capable of being removed by water or a solventand the second layer 204 provided thereon and formed of a curing resincapable of being cured by light or heat can be provided on not only theamplitude type hologram layer with a metal film patterned thereon butalso a hologram layer comprising a photopolymer or other hologramphotosensitive material layer with interference fringes recordedtherein.

[0118] It is not always necessary to provide such layers directly on thehologram layer 202. In the replication process using a spacer forinstance, the first layer 203 capable of being removed by water or asolvent and the second layer 204 provided thereon and formed of a curingresin capable of being cured by light or heat may be formed on thesurface of the spacer.

[0119] While the hologram plate and its fabrication process of thepresent invention have been described with reference to some specificembodiments, it is understood that the present invention is not limitedthereto, and so many modifications may be made.

[0120] In the present invention for the purpose of achieving theaforesaid first object, the hologram plate comprises a multilayerstructure made up of a first transparent substrate, a hologram layer, anadhesive layer and a second transparent layer and the second transparentsubstrate defines a surface in contact with a hologram photosensitivematerial during hologram replication, so that the second transparentsubstrate can function as a protective layer to make the hologram plateresistant to marring. In addition, the second transparent substrate canbe used as a spacer for the double-focus replication process wherein thedistance between the hologram plate and the hologram photosensitivematerial is set at substantially double the focal length of eachcollective element hologram, so that replicas can be fabricated withconstant focal lengths.

[0121] An absorbing layer is located between the hologram layer and theadhesive layer or at other position to allow the zero-order light andfirst-order light diffracted by the hologram layer to have substantiallythe same intensity, so that hologram replicas of high diffractionefficiency can be obtained.

[0122] According to the present invention for achieving the aforesaidsecond object, all the unit holograms can be precisely replicatedbecause the unit hologram segments are kept flush with one another byone common thin sheet glass provided over the plurality of juxtaposedunit hologram segments. When the hologram photosensitive material isbrought into close contact with the multifaceted hologram plate with anindex matching liquid applied therebetween for the purpose of hologramreplication, it is extremely unlikely that an optical adhesive agentbetween adjacent unit hologram segments will be dissolved in the indexmatching liquid. If a glass sheet is used as the transparent thin sheet,improved durability is then obtained. Fabricated by the lamination ofonly unit hologram segments put in good alignment with good properties,the multifaceted hologram plate according to the present invention forachieving the aforesaid second object have all unit hologram segments ofgood quality and uniform properties, and so can be used for hologramreplication with high efficiency.

[0123] According to the present invention for achieving the aforesaidthird object, there is provided a hologram plate comprising a hologramlayer with interference fringes formed thereon, a first layer capable ofbeing removed with water or a solvent, which is provided on the surfaceof said hologram layer or a transparent layer formed thereon, and asecond layer of a curing resin capable of being cured by light or heat,which is formed on said first layer. The second layer functions as aprotective layer for the hologram layer thereby preventing the marring,wearing and contamination of the hologram layer, which may otherwiseoccur at steps of coating an index matching liquid, carrying out contactreplication, removing the index matching liquid, removing foreignmatters, and so on. As many holograms are replicated, the second layer,too, is subjected to marring, wearing and contamination. In this caseor, for instance, when one fails to form the first layer or the secondlayer, the hologram plate is washed with water or boiled in boilingwater, so that the protective layer can be easily removed. Then, iffresh first and second layers are provided on the hologram layer, thehologram plate can be regenerated.

[0124] The hologram plate for achieving the third object of the presentinvention comprises a hologram layer with interference fringes formedthereon, a first layer capable of being removed with water or a solvent,which is provided on the surface of said hologram layer or a transparentlayer formed thereon, and a second layer of a curing resin capable ofbeing cured by light or heat, which is formed on said first layer. Thesecond layer functions as a protective layer for the hologram layer,thereby preventing the marring, wearing and contamination of thehologram layer, which may otherwise occur at steps of coating an indexmatching liquid, carrying out contact replication, removing the indexmatching liquid, removing foreign matters, and so on. As many hologramsare replicated, the second layer, too, is subjected to marring, wearingand contamination. In this case or, for instance, when one fails to formthe first layer or the second layer, the hologram plate is washed withwater or boiled in boiling water, so that the protective layer can beeasily removed. Then, if fresh first and second layers are provided onthe hologram layer, the hologram plate can be regenerated.

What we claim is:
 1. A hologram plate comprising an array of atransmission type of collective element holograms that diffract parallellight incident thereon at a specific wavelength and a specific incidentangle in such a way that the parallel light is converged on a specificfocal length position, which comprises a multilayer structure made up ofa first transparent substrate, a hologram layer, an adhesive layer and asecond transparent substrate, said second transparent substrate defininga surface in contact with a hologram photosensitive material whenhologram replication is carried out.
 2. The hologram plate according toclaim 1 , wherein said second transparent substrate has a thicknesssubstantially double the focal length of each collective elementhologram, inclusive of the thickness of said adhesive layer.
 3. Thehologram plate according to claim 1 , wherein between said hologramlayer and said adhesive layer there is interleaved a water-solubleprotective layer.
 4. The hologram plate according to claim 3 , whereinsaid second transparent substrate has a thickness substantially doublethe focal length of each collective element hologram, inclusive of thethicknesses of said adhesive layer and said water-soluble protectivelayer.
 5. The hologram plate according to any one of claims 1 to 4 ,wherein said hologram layer has a diffraction efficiency preset in sucha way as to allow zero-order light and first-order light diffracted bysaid hologram layer to have substantially the same intensity.
 6. Thehologram plate according to any one of claims 1 to 5 , wherein anabsorbing layer is located at any desired position between said hologramlayer and said second transparent layer, and a light-absorbing materialis dispersed throughout said absorbing layer in such a way so as toallow zero-order light and first-order light diffracted by said hologramlayer to have substantially the same intensity.
 7. The hologram plateaccording to any one of claims 1 to 5 , wherein an absorbing layer islocated on the surface of said second transparent layer, and alight-absorbing material is dispersed throughout said absorbing layer insuch a way so as to allow zero-order light and first-order lightdiffracted by said hologram layer to have substantially the sameintensity.
 8. A process for fabricating a hologram plate comprising anarray of a transmission type of collective element holograms thatdiffract parallel light incident thereon at a specific wavelength and aspecific incident angle in such a way that the parallel light isconverged on a specific focal length position, said hologram platecomprising a multilayer structure made up of a first transparentsubstrate, a hologram layer, an adhesive layer and a second transparentsubstrate, and said second transparent substrate defining a surface incontact with a hologram photosensitive material when hologramreplication is carried out, wherein: said adhesive layer comprises anultraviolet curing adhesive agent, said multilayer structure, obtainedby forming said hologram layer on said first transparent substrate andthen superposing said second transparent substrate on said hologramlayer with an uncured ultraviolet curing adhesive agent interleavedtherebetween, is spun to spin an extra portion of said adhesive agentout of the periphery thereof, thereby making said adhesive layeruniform, while the rpm of said multilayer structure is controlled toobtain a desired thickness, and said multilayer structure is irradiatedwith ultraviolet radiation through said first transparent substrate orsaid second transparent substrate to cure said adhesive agent.
 9. Thehologram plate fabrication process according to claim 8 , wherein saidhologram is exposed to p-polarized light.
 10. The hologram platefabrication process according to claim 8 , wherein said hologram isexposed to s-polarized light.
 11. A hologram plate comprising aplurality of juxtaposed unit hologram segments, wherein: one commontransparent thin sheet is provided over the surfaces of said pluralityof juxtaposed unit hologram segments with an adhesive agent interleavedtherebetween.
 12. The hologram plate according to claim 11 , whereineach unit hologram segment comprises a transparent substrate, aphotosensitive material layer formed thereon while a hologram isrecorded therein, and a protective layer formed on said photosensitivematerial layer.
 13. The hologram plate according to claim 12 , wherein atransparent thin sheet is bonded onto said protective layer for eachunit hologram segment.
 14. The hologram plate according to any one ofclaims 11 to 13 , wherein said plurality of unit hologram segments arehologram segments replicated from the same hologram plate.
 15. Thehologram plate according to any one of claims 11 to 14 , wherein eachunit hologram segment comprises a hologram color filter.
 16. A processfor fabricating a hologram plate comprising a plurality of juxtaposedunit hologram segments and one common transparent sheet provided overthe surfaces of said unit hologram segments with an adhesive agentinterleaved therebetween, which comprises steps of: preparing aplurality of unit hologram segments, adsorbing a transparent thin sheetonto the surface of a reference plate and laminating said plurality ofunit hologram segments, in juxtaposed relation to each other, on saidtransparent thin sheet with an adhesive agent interleaved therebetween,bonding a base plate onto the back side of said plurality of juxtaposedunit hologram segments with an adhesive agent interleaved therebetween,and desorbing said transparent thin sheet from said reference plate torelease said transparent thin sheet from said reference plate.
 17. Thehologram plate fabrication process according to claim 16 , wherein atthe step of preparing a plurality of unit hologram segments, saidplurality of unit hologram segments are hologram segments replicatedfrom the same hologram plate.
 18. A hologram plate comprising a hologramlayer with interference fringes formed thereon, a first layer capable ofbeing removed with water or a solvent, which is provided on the surfaceof said hologram layer or a transparent layer formed thereon, and asecond layer of a curing resin capable of being cured by light or heat,which is formed on said first layer.
 19. The hologram plate according toclaim 18 , wherein said hologram layer is an amplitude type hologramlayer with a metal film patterned thereon.
 20. The hologram plateaccording to claim 18 , wherein said hologram layer is a hologram layercomprising a hologram photosensitive material layer with interferencefringes recorded therein.
 21. The hologram plate according to any one ofclaims 18 to 20 , wherein said first layer is capable of absorbinglight.
 22. The hologram plate according to any one of claims 18 to 21 ,which comprises a transmission type hologram.
 23. The hologram plateaccording to any one of claims to 21, which comprises a reflection typehologram.